Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery including a positive electrode formed of a positive electrode active material including first positive electrode active material particles and second positive electrode active material particles, a negative electrode, and a separator layer interposed between the positive electrode and the negative electrode. The first positive electrode active material particles include a lithium metal oxide in which at least one metal forms a concentration gradient. The second positive electrode active material particles include primary particles having shapes or crystal structures different from each other.

Description

[0001] This application is a divisional application of Chinese Patent Application No. 201910602973.5, filed on July 5, 2019, entitled "Lithium Secondary Battery". This application claims priority to Korean Patent Application Nos. 10-2018-0078843 and 10-2018-0078844, filed with the Korean Intellectual Property Office (KIPO) on July 6, 2018, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to lithium secondary batteries. More specifically, this invention relates to lithium secondary batteries comprising lithium metal oxide. Background Technology

[0003] With the development of information and display technologies, rechargeable and dischargeable secondary batteries have been widely used as power sources for mobile electronic devices such as camcorders, mobile phones, and portable computers. Recently, battery packs incorporating secondary batteries are being developed for use as power sources in environmentally friendly vehicles such as hybrid electric vehicles.

[0004] Secondary batteries include, for example, lithium-ion batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Lithium-ion batteries have attracted much attention due to their high operating voltage and energy density per unit weight, high charge rate, and small size.

[0005] For example, a lithium secondary battery may include electrode assemblies and an electrolyte impregnating the electrode assemblies, the electrode assemblies including a cathode, an anode, and a separation layer. A lithium secondary battery may also include a casing having, for example, a pouch shape.

[0006] Lithium metal oxides can be used as positive electrode active materials for lithium secondary batteries, which preferably have high capacity, power, and lifespan. Furthermore, with the expansion of industrial applications of lithium secondary batteries, the stability of lithium secondary batteries or positive electrode active materials under harsh conditions at high or low temperatures is also required. In addition, resistance to faults such as short circuits, fires, or explosions is also necessary when lithium secondary batteries or positive electrode active materials are penetrated by external objects.

[0007] However, positive electrode active materials possessing all the aforementioned properties may not be readily available. For example, Korean Patent Application No. 10-2017-0093085 discloses a positive electrode active material comprising a transition metal compound and an ion-adsorbent binder, which may not provide sufficient lifetime and stability. Summary of the Invention

[0008] According to one aspect of the present invention, a lithium secondary battery is provided, which has improved electrical and mechanical reliability and safety.

[0009] According to an exemplary embodiment, a lithium secondary battery includes a positive electrode, a negative electrode, and an insulating layer between the positive and negative electrodes, formed of a positive electrode active material comprising first positive electrode active material particles and second positive electrode active material particles. The first positive electrode active material particles comprise lithium metal oxide, wherein at least one metal in the lithium metal oxide forms a concentration gradient. The second positive electrode active material particles comprise primary particles having different shapes or crystal structures from each other.

[0010] In some embodiments, the second positive electrode active material particles may include a first particle disposed in a central region and a second particle disposed in a peripheral region, and the first particle and the second particle have different shapes or crystal structures from each other.

[0011] In some implementations, the first particle may have a granular or spherical structure, and the second particle may have a rod-shaped or needle-shaped shape.

[0012] In some embodiments, the central region of the second positive electrode active material particle may include a region corresponding to 20%-80% of the radius from the center of the second positive electrode active material particle.

[0013] In some embodiments, the first positive electrode active material particle may include a core portion, a shell portion, and a concentration gradient region located between the core portion and the shell portion, wherein a concentration gradient may be formed in the concentration gradient region.

[0014] In some implementations, the core portion and the shell portion may each include fixed components.

[0015] In some embodiments, the first positive electrode active material particle may include a continuous concentration gradient formed from the center of the first positive electrode active material particle to the surface of the first positive electrode active material particle.

[0016] In some implementations, the first positive electrode active material particle may be represented by the following chemical formula 1.

[0017] [Chemical Formula 1]

[0018] Li x M1 a M2 b M3 c O y

[0019] In Chemical Formula 1, M1, M2 and M3 are selected from Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga and B, 0<x≤1.1, 1.98≤y≤2.02, 0<a<1, 0<b<1, 0<c<1, and 0<a+b+c<1.

[0020] In some embodiments, in Chemical Formula 1, 0.6≤a≤0.95, and 0.05≤b+c≤0.4.

[0021] In some embodiments, in Chemical Formula 1, 0.7≤a≤0.9, and 0.1≤b+c≤0.3.

[0022] In some embodiments, M1 may be nickel (Ni), M2 may be manganese (Mn), and M3 may be cobalt (Co).

[0023] In some embodiments, the second positive electrode active material particle may be represented by the following Chemical Formula 2.

[0024] [Chemical Formula 2]

[0025] Li x Ni a Co b Mn c M4 d M5 e O y

[0026] In Chemical Formula 2, M4 may include at least one element selected from the group consisting of Ti, Zr, Al, Mg and Cr; M5 may include at least one element selected from the group consisting of Sr, Y, W and Mo; 0<x<1.5, 1.98≤y≤2.02, 0.313≤a≤0.353, 0.313≤b≤0.353, 0.313≤c≤0.353, 0≤d≤0.03, 0≤e≤0.03, and 0.983≤a+b+c≤1.02.

[0027] In some embodiments, the second positive electrode active material particles may include lithium metal oxide having excess lithium and at least two metal elements other than lithium.

[0028] In some embodiments, the second positive electrode active material particle may be represented by the following Chemical Formula 3.

[0029] [Chemical Formula 3]

[0030] Li x Ni α Co β Mn γ M4 δM5 ε O y

[0031] In Chemical Formula 3, M4 may comprise at least one element selected from the group consisting of Ti, Zr, Al, Mg and Cr; M5 may comprise at least one element selected from the group consisting of Sr, Y, W and Mo; 0<x<1.1, 1.98≤y≤2.02, 0.48≤α≤0.52, 0.18≤β≤0.27, 0.24≤γ≤0.32, 0≤δ≤0.03, 0≤ε≤0.03, and 0.98≤α+β+γ≤1.02.

[0032] In some embodiments, in Chemical Formula 3, 0.49≤α≤0.51, 0.18≤β≤0.22, and 0.28≤γ≤0.32.

[0033] In some embodiments, a blending weight ratio of the first positive electrode active material particles and the second positive electrode active material particles may be 9:1 to 1:9.

[0034] In some embodiments, in differential scanning calorimetry (DSC) measurement, an exothermic peak of the second positive electrode active material particles is 40 J / g or less at a temperature of 200° C. or higher.

[0035] According to the exemplary embodiment as described above, a positive electrode active material for a lithium secondary battery may include first positive electrode active material particles having a concentration gradient and second positive electrode active material particles having a multi-shaped structure. High capacity and high power output characteristics of the lithium secondary battery can be achieved by the first positive electrode active material particles. High output, penetration safety and thermal stability of the lithium secondary battery can be achieved by the second positive electrode active material particles. In addition, penetration stability at a high state of charge (SoC) can be improved.

[0036] Therefore, electrical performance and mechanical safety of the lithium secondary battery can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a schematic cross-sectional view illustrating a lithium secondary battery according to an exemplary embodiment.

[0038] Figure 2-6 are cross-sectional SEM (scanning electron microscope) images of second positive electrode active material particles used in some examples and comparative examples;

[0039] Figure 7 are Figure 2 and 3 differential scanning calorimetry (DSC) curves of the second positive electrode active material particles shown in; and

[0040] Figure 8 are Figure 4-6 The DSC diagram of the second positive electrode active material particles is shown. Detailed Implementation

[0041] According to an exemplary embodiment of the present invention, a lithium secondary battery is provided, which includes a first positive electrode active material particle having a concentration gradient and a second positive electrode active material particle having a multi-shaped structure as positive electrode active materials, and has improved electrical performance and mechanical safety.

[0042] The invention will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that these embodiments described with reference to the drawings are provided to further understand the spirit of the invention and are not intended to limit the subject matter claimed in the specification and appended claims.

[0043] The terms “first” and “second” used in this article are not intended to specify the number or order of objects, and are only used to identify different elements or objects.

[0044] Figure 1 A schematic cross-sectional view is provided to illustrate a lithium secondary battery according to an exemplary embodiment.

[0045] See Figure 1 The lithium secondary battery may include a positive electrode 130, a negative electrode 140, and an insulating layer 150 between the positive electrode 130 and the negative electrode 140.

[0046] The positive electrode 130 may include a positive electrode current collector 110 and a positive electrode active material layer 115 formed by coating the positive electrode current collector 110 with a positive electrode active material.

[0047] In an exemplary embodiment, the positive electrode active material may include a first positive electrode active material particle and a second positive electrode active material particle, and may be formed by mixing the first positive electrode active material particle and the second positive electrode active material particle.

[0048] The first positive electrode active material particles may have a concentration gradient. For example, the first positive electrode active material particles may include lithium metal oxide, wherein at least one metal element forms a concentration gradient. The lithium metal oxide may include nickel and other transition metals, and may include an excess of nickel among the metal elements other than lithium. As used herein, the term "excess" refers to the maximum content or molar ratio of the metal elements other than lithium.

[0049] In an exemplary embodiment, the first positive electrode active material particle may include a concentration gradient region located between the central portion and the surface. For example, the concentration gradient region may be formed in a specific region between the central portion and the surface.

[0050] In an exemplary embodiment, the first positive electrode active material particle may include a core portion and a shell portion, with a concentration gradient region between the core portion and the shell portion. For example, the core portion may include a central portion, and the shell portion may include a surface.

[0051] A concentration gradient of certain metal elements with respect to the lithium metal oxide can be formed in the concentration gradient region. The concentration can be uniform or fixed in both the core and shell portions. For example, the lithium metal oxide in both the core and shell portions can have a substantially fixed composition.

[0052] In some embodiments, the concentration gradient region may be formed at the central portion. In some embodiments, the concentration gradient region may be formed at the surface.

[0053] In some implementations, the concentrations of lithium and oxygen can be substantially constant throughout the entire region of the particle, and at least one element other than lithium and oxygen can have a continuous concentration gradient.

[0054] The term "continuous concentration gradient" as used herein can refer to a concentration curve that can change with a uniform trend or tendency between the central and surface portions. A uniform trend can include an increasing trend or a decreasing trend.

[0055] In some embodiments, the first positive electrode active material particle may comprise a lithium metal oxide having a continuous concentration gradient from the center portion of the particle to the particle surface. For example, the concentration gradient region may be formed over the entire diameter or radius from the center to the surface of the first positive electrode active material particle. In some embodiments, the first positive electrode active material particle may have a full concentration gradient (FCG) structure, wherein the concentration gradient may be formed substantially throughout the entire particle.

[0056] As used herein, the term "central portion" may include the center point of an active material particle, and may also include a region within a predetermined radius or diameter from the center point. For example, "central portion" may include a region within a radius of approximately 0.1 μm from the center point of an active material particle.

[0057] As used herein, the term "surface portion" may include the outermost surface of an active material particle and may also include a predetermined thickness from the outermost surface. For example, "surface portion" may include a region within a thickness of approximately 0.1 μm from the outermost surface of the active material particle.

[0058] In some implementations, continuous concentration particles may include a linear concentration profile or a curved concentration profile. In a curved concentration profile, the concentration may change with a uniform trend without any inflection points.

[0059] In one embodiment, at least one metal other than lithium contained in the first positive electrode active material particle may have an increasing continuous concentration gradient, and at least one metal other than lithium contained in the first positive electrode active material particle may have a decreasing continuous concentration gradient.

[0060] In one embodiment, at least one metal other than lithium contained in the first positive electrode active material particle may have a substantially constant concentration from the central portion to the surface.

[0061] In one embodiment, the at least one metal other than lithium contained in the first positive electrode active material particle may include a first metal M1 and a second metal M2. The first metal M1 may have a continuously decreasing concentration gradient from the central portion to the surface. The second metal M2 has a continuously increasing concentration gradient from the central portion to the surface.

[0062] In one embodiment, the at least one metal other than lithium contained in the first positive electrode active material particle may further include a third metal M3. The third metal M3 may have a substantially constant concentration from the central portion to the surface.

[0063] As used herein, the term "concentration" may refer to, for example, the molar ratio of the first metal to the third metal.

[0064] For example, the first positive electrode active material particle may be represented by the following Chemical Formula 1.

[0065] [Chemical Formula 1]

[0066] Li x M1 a M2 b M3 c O y

[0067] In the above Chemical Formula 1, M1, M2 and M3 are each selected from the group consisting of Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga and B, 0<x≤1.1, 1.98≤y≤2.02, 0<a<1, 0<b<1, 0<c<1, and 0<a+b+c<1.

[0068] In some embodiments, M1, M2 and M3 in Chemical Formula 1 may be nickel (Ni), manganese (Mn) and cobalt (Co), respectively.

[0069] For example, nickel can be used as a metal related to the capacity of lithium-ion batteries. As the amount of nickel increases, the capacity and power of the lithium-ion battery can be improved. However, excessive nickel can reduce battery life performance and may be detrimental to the battery's mechanical and electrical stability. For instance, when the amount of nickel is excessively increased, it may not be able to adequately suppress defects such as fires or short circuits caused by penetration by external objects.

[0070] However, according to an exemplary embodiment, nickel may be included as the first metal M1. Therefore, the amount of nickel at the central portion may be relatively high to improve the capacity and power of the lithium secondary battery, and the nickel concentration may decrease from the central portion to the surface to prevent defects and reduced lifespan due to penetration.

[0071] For example, manganese (Mn) can be used as a metal related to the mechanical and electrical stability of lithium secondary batteries. In an exemplary embodiment, the amount of Mn can be increased from the central portion to the surface, thereby suppressing or reducing defects caused by surface penetration, such as fires or short circuits, and also increasing the lifespan of the lithium secondary battery.

[0072] For example, cobalt (Co) can be used as a metal related to the conductivity or resistance of lithium secondary batteries. In an exemplary embodiment, the concentration of cobalt can be fixed or uniformly maintained throughout the entire region of the first positive electrode active material particles. Therefore, the current or charge flow through the first positive electrode active material particles can be uniformly maintained, while improving the battery's conductivity and maintaining low resistance.

[0073] In some embodiments, in Formula 1, the first metal M1 may be nickel, and for example 0.6 ≤ a ≤ 0.95, 0.05 ≤ b + c ≤ 0.4. For example, the concentration (or molar ratio) of nickel may be continuously reduced from about 0.95 to about 0.6.

[0074] If the lower limit of nickel concentration (e.g., surface concentration) is less than about 0.6, the capacity and power at the surface of the first cathode active material particles may be excessively degraded. If the upper limit of nickel concentration (e.g., center concentration) exceeds about 0.95, the lifetime and mechanical stability of the center portion may be excessively reduced.

[0075] Preferably, in chemical formula 1, 0.7 ≤ a ≤ 0.9, and 0.1 ≤ b + c ≤ 0.3. In this case, the battery capacity and stability can be enhanced.

[0076] In an exemplary embodiment, the first positive electrode active material particle may include a concentration gradient region, wherein at least one metal forms a concentration gradient between a central portion and a surface. For example, the concentration gradient may include a specific region located between the central portion and the surface. The first positive electrode active material particle may have a fixed concentration distribution in regions other than the concentration gradient region.

[0077] In some embodiments, the first metal (M1), the second metal (M2), and the third metal (M3) may have the aforementioned concentration distribution within the concentration gradient region. In some embodiments, the concentration gradient region may be formed at the central portion. In some embodiments, the concentration gradient region may be formed at the surface.

[0078] In some embodiments, the first positive electrode active material particles may also include a coating on their surface. For example, the coating may include Al, Ti, Ba, Zr, Si, B, Mg, P, alloys thereof, or oxides thereof. These may be used alone or in combination. The first positive electrode active material particles can be protected by the coating, thereby further improving the battery's penetration stability and lifespan.

[0079] In some implementations, the elements, alloys, or oxides of the coating may be incorporated as dopants into the first positive electrode active material particles.

[0080] In some embodiments, the first positive electrode active material particles may be formed from primary particles having a rod-shaped form. The average diameter of the first positive electrode active material particles may be in the range of about 3 μm to about 25 μm.

[0081] For example, high capacity and / or high output characteristics can be achieved by using first cathode active material particles containing lithium metal oxide (in which nickel is used in excess). Furthermore, a concentration gradient can be included in the first cathode active material to suppress degradation of lifetime and operational stability due to the use of excess nickel.

[0082] According to an exemplary embodiment, since the second positive electrode active material particles with a multi-shaped structure can be blended with the first positive electrode active material particles, the penetration safety or resistance characteristics of the lithium secondary battery can be significantly improved.

[0083] For example, if a positive electrode active material containing an excess of nickel can be used alone, a fire or explosion may occur when the secondary battery is penetrated by an external object, as the overcurrent generates a large amount of heat in a short time.

[0084] According to an exemplary embodiment, a second positive electrode active material having a multi-shape structure can be blended with a first positive electrode active material. In this case, even if the secondary battery is penetrated, the heat generated due to overcurrent is suppressed to prevent fire or explosion.

[0085] For example, since the second positive electrode active material particles may include primary particles with different particle shapes, the internal structure of the positive electrode active material particles can be irregular. Particles with different shapes can act as resistors between each other, thereby suppressing excessive heat progression.

[0086] According to an exemplary embodiment, the second positive electrode active material particles may have a multi-shape structure. The term "multi-shape" as used herein differs from "single-shape" and may refer to a cohesive structure of particles of different shapes.

[0087] For example, the second positive electrode active material particles may have a secondary particle structure formed by the aggregation of primary particles. The second positive electrode active material particles may include multiple primary particles having different shapes or crystal structures from each other.

[0088] In some embodiments, the second positive electrode active material particle (e.g., a primary particle contained in the second positive electrode active material particle) may include a first particle and a second particle having different shapes or crystal structures from each other.

[0089] For example, the first and second particles can have various shapes, such as granular, spherical, elliptical, rod-shaped and needle-shaped, and can have different shapes or crystal structures from each other.

[0090] The first particle can be arranged in the central region of the second positive electrode active material particle, and the second particle can be arranged in the peripheral region of the second positive electrode active material particle.

[0091] For example, the central region may include a region corresponding to a length of about 20% to about 80% of the radius from the center to the second positive electrode active material particle. The peripheral region may surround the remaining region outside the central region. In some embodiments, the central region may include a region corresponding to a length of about 40% to about 70% of the radius from the center to the second positive electrode active material particle.

[0092] In some embodiments, the first particle disposed in the central region may have a granular or spherical structure, and the second particle disposed in the peripheral region may have a rod-like or needle-like structure. In this case, conductivity and capacitance characteristics can be achieved in the peripheral region by the second particle, and rapid heat propagation in the central region can be effectively prevented by the first particle.

[0093] According to an exemplary embodiment, the second positive electrode active material particle may include lithium metal oxide. In an exemplary embodiment, the second positive electrode active material particle may include nickel-containing lithium metal oxide. The nickel concentration in the second positive electrode active material particle may be lower than the nickel concentration in the first positive electrode active material particle. In some embodiments, the nickel concentration in the second positive electrode active material particle may be fixed to be lower than the nickel concentration on the surface of the first positive electrode active material particle.

[0094] In some embodiments, the second positive electrode active material particles may comprise at least two metal elements other than lithium. For example, the concentration of the metal other than lithium may remain constant from the central portion to the surface.

[0095] In some embodiments, the second positive electrode active material particles may include a first metal M1', a second metal M2' and a third metal M3'. For example, the first metal M1', the second metal M2' and the third metal M3' may be nickel, cobalt and manganese, respectively.

[0096] In some embodiments, the concentrations or molar ratios of nickel, cobalt and manganese can remain uniform throughout the entire region of the second positive electrode active material particles.

[0097] In an exemplary embodiment, the second positive electrode active material particles may be represented by the following Chemical Formula 2.

[0098] [Chemical Formula 2]

[0099] Li x Ni a Co b Mn c M4 d M5 e O y

[0100] In Chemical Formula 2, M4 may include at least one element selected from Ti, Zr, Al, Mg and Cr; M5 may include at least one element selected from Sr, Y, W and Mo; 0<x<1.5, 1.98≤y≤2.02, 0.313≤a≤0.353, 0.313≤b≤0.353, 0.313≤c≤0.353, 0≤d≤0.03, 0≤e≤0.03, and 0.98≤a+b+c≤1.02.

[0101] By controlling the contents or molar ratios of nickel, cobalt and / or manganese in the second positive electrode active material to be substantially the same, the thermal stability and mechanical properties, such as cycle life stability and penetration safety, can be improved through the second positive electrode active material.

[0102] According to some exemplary embodiments, when the second positive electrode active material particles represented by Chemical Formula 2 are measured by differential scanning calorimetry (DSC), the particles may exhibit an exothermic peak of 40 J / g or less at a temperature above 200°C. According to some embodiments, in the DSC method, the second positive electrode active material particles may exhibit an exothermic peak of 15 J / g or less at a temperature above 320°C.

[0103] In some embodiments, in consideration of the capacity and stability of a lithium secondary battery, the second positive electrode active material particles may include an excess amount of nickel, and the concentration may be controlled in the order of nickel, manganese and cobalt. According to an exemplary embodiment, a concentration ratio of nickel:cobalt:manganese in the second positive electrode active material particles may be substantially about 5:2:3.

[0104] In an exemplary embodiment, the second positive electrode active material particles may be lithium nickel-cobalt-manganese oxide represented by Chemical Formula 3 below.

[0105] [Chemical Formula 3]

[0106] Li x Ni α Co β Mn γ M4 δ M5 ε O y

[0107] In Chemical Formula 3, M4 includes at least one element selected from Ti, Zr, Al, Mg and Cr; M5 includes at least one element selected from Sr, Y, W and Mo; 0<x<1.1, 1.98≤y≤2.02, 0.48≤α≤0.52, 0.18≤β≤0.27, 0.24≤γ≤0.32, 0≤δ≤0.03, 0≤ε≤0.03, and 0.98≤α+β+γ≤1.02.

[0108] In some embodiments, in Chemical Formula 3, 0.49≤α≤0.51, 0.18≤β≤0.22, and 0.28≤γ≤0.32.

[0109] For example, the nickel concentration or the nickel mole ratio of the second positive electrode active material particles may be less than that of the first positive electrode active material particles throughout the entire region of the particles, and Mn may be uniformly distributed in all of the second positive electrode active material particles. By controlling the contents or mole ratios of nickel, cobalt and / or manganese of the second positive electrode active material to 5:2:3 respectively, thermal properties and mechanical properties such as life stability and penetration safety can be improved by the second positive electrode active material.

[0110] According to some exemplary embodiments, when the second positive electrode active material particles represented by Chemical Formula 3 are measured by differential scanning calorimetry (DSC), an exothermic peak of 25 J / g or less may be exhibited at a temperature of 200°C or higher. According to some embodiments, in the DSC method, the second positive electrode active material particles may exhibit an exothermic peak of 25 J / g or less at a temperature of 330°C or higher.

[0111] In some embodiments, the second positive electrode active material particles may further include a coating on their surface. For example, the coating may include Al, Ti, Ba, Zr, Si, B, Mg, P, their alloys, their oxides, their phosphates, or their fluorides. The first positive electrode active material particles can be protected by the coating, thereby further improving the battery's penetration stability and lifespan. By further including a coating, the capacity and power output characteristics of the positive electrode active material can be improved.

[0112] In some implementations, the elements, alloys, or oxides of the coating can be incorporated as dopants into the particles of the second positive electrode active material.

[0113] In some implementations, the positive electrode active material can be prepared by manufacturing each of the first positive electrode active material particles and the second positive electrode active material particles, and then mixing the first positive electrode active material particles and the second positive electrode active material particles.

[0114] In an exemplary embodiment, the mixing ratio of the first positive electrode active material particles and the second positive electrode active material particles can be, for example, 9:1 to 1:9, preferably 6:4 to 1:9. Within the above range, the second positive electrode active material particles can more effectively improve thermal stability and prevent ignition caused by penetration, and can achieve high-density characteristics of the secondary battery.

[0115] Preferably, if the second positive electrode active material particles represented by Formula 2 are used, the mixing weight ratio can be 6:4-9:1. When using the second positive electrode active material particles represented by Formula 3, the mixing weight ratio can be 6:4-3:7.

[0116] In the formation of the first positive electrode active material particles, metal precursor solutions with different concentrations can be prepared. The metal precursor solutions may include precursors of metals that can be contained in the positive electrode active material. For example, metal precursors may include metal halides, hydroxides, acid salts, etc.

[0117] For example, metal precursors may include lithium precursors (e.g., lithium oxide), nickel precursors, manganese precursors, and cobalt precursors.

[0118] In some embodiments, a first precursor solution having a target composition at the central portion (e.g., the concentration of nickel, manganese, and cobalt at the central portion) and a second precursor solution having a target composition at the surface or surface portion (e.g., the concentration of nickel, manganese, and cobalt at the surface) can be prepared separately.

[0119] Subsequently, the first precursor solution and the second precursor solution can be mixed, and a precipitate can be formed by co-precipitation. In some embodiments, the mixing ratio can be continuously varied, such that a continuous concentration gradient can be formed from the target composition at the central portion to the target composition at the surface. Therefore, the precipitate can contain a concentration gradient including the metal.

[0120] In some embodiments, a chelating agent and an alkaline reagent (e.g., a base reagent) may be added during precipitate formation. In some embodiments, the precipitate may be heat-treated, and then a lithium salt may be incorporated and heat-treated again.

[0121] Second cathode active material particles can be formed by precipitating a single metal precursor solution with a target composition while stirring. During the precipitation process, by changing the flow rate, composition, concentration, temperature, and stirring speed of the precursor solution, multi-shape structures with various shapes or crystal structures can be prepared.

[0122] In an exemplary embodiment, the positive electrode active material may be mixed with a binder, conductive additives, and / or dispersing additives in a solvent and stirred to form a slurry. The slurry may be coated onto the positive electrode current collector 110, pressed, and dried to obtain the positive electrode 130.

[0123] The positive electrode current collector 110 may comprise a metal that has high conductivity, can readily adhere to the active material slurry, and is non-reactive within the voltage range of the battery. The positive electrode current collector 110 may comprise stainless steel, nickel, aluminum, titanium, copper, or alloys thereof. Preferably, aluminum or alloys thereof may be used.

[0124] The adhesive may include organic adhesives such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, etc., or water-based adhesives such as styrene-butadiene rubber (SBR), which may be used with thickeners such as carboxymethyl cellulose (CMC).

[0125] For example, a PVDF-based binder can be used as the positive electrode binder. In this case, the amount of binder used to form the positive electrode active material layer 115, as well as the amount of the first positive electrode active material particles and the second positive electrode active material particles, can be relatively increased. Therefore, the capacity and power output of the lithium secondary battery can be further improved.

[0126] Conductive additives can be added to promote electron migration between active material particles. For example, conductive additives may include carbon-based materials such as graphite, carbon black, graphene, carbon nanotubes, etc., and / or metal-based materials such as tin, tin oxide, titanium oxide, perovskite materials (e.g., LaSrCoO3 or LaSrMnO3).

[0127] In an exemplary embodiment, the negative electrode 140 may include a negative electrode current collector 120 and a negative electrode active material layer 125 formed by coating a negative electrode active material onto the negative electrode current collector 120.

[0128] The negative electrode active material may include materials capable of adsorbing and desorbing lithium ions. For example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon complexes or carbon fibers, lithium alloys, silicon, tin, etc., may be used. Amorphous carbon may include hard carbon, coke, mesophase carbon microspheres (MCMB) calcined at 1500°C or lower, mesophase pitch-based carbon fibers (MPCF), etc. Crystalline carbon may include graphite-based materials, such as natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc. Lithium alloys may further include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0129] The negative electrode current collector 110 may include a metal that has high conductivity and can easily adhere to the active material slurry and is non-reactive within the voltage range of the battery. The negative electrode current collector 120 may include gold, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, preferably copper or copper alloys.

[0130] In some embodiments, the negative electrode active material may be mixed with a binder, conductive additives, and / or dispersing additives in a solvent and stirred to form a slurry. The slurry may be coated onto the negative electrode current collector 120, pressed, and dried to obtain the negative electrode 140.

[0131] Adhesives and conductive additives that are substantially the same or similar to those described above can be used. In some embodiments, the adhesive for the negative electrode 140 may include an aqueous adhesive such as styrene-butadiene rubber (SBR), which may be used with a thickener such as carboxymethyl cellulose (CMC) to improve compatibility with carbon-based active materials.

[0132] The separator 150 can be inserted between the positive electrode 130 and the negative electrode 140. The separator 150 may include a porous polymer membrane made of, for example, a polyolefin-based polymer, such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc. The separator 150 may also be formed of a nonwoven fabric, including high-melting-point glass fiber, polyethylene terephthalate fiber, etc.

[0133] In some embodiments, the area and / or volume of the negative electrode 140 (e.g., the contact area with the separator 150) may be larger than the area and / or volume of the positive electrode 130. Therefore, lithium ions generated from the positive electrode 130 can be readily transferred to the negative electrode 140 without loss due to, for example, precipitation or sedimentation. Thus, enhanced power and stability can be effectively achieved through the combination of the first and second positive electrode active material particles.

[0134] In an exemplary embodiment, electrode unit 160 may be defined by a positive electrode 130, a negative electrode 140, and a separator 150, and multiple electrode units 160 may be stacked to form an electrode assembly having, for example, a jelly roll shape. For example, the electrode assembly may be formed by winding, laminating, or folding the insulating layer 150.

[0135] The electrode assembly may be housed together with the electrolyte in the housing 170 to form a lithium secondary battery. In an exemplary embodiment, the electrolyte may include a non-aqueous electrolyte solution.

[0136] Non-aqueous electrolyte solutions may include lithium salts and organic solvents. Lithium salts can be derived from Li... + X - This indicates that the lithium salt anion X - It may include, for example, F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - (CF3CF2SO2)2N - wait.

[0137] Organic solvents may include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, tetrahydrofuran, etc. These organic solvents may be used alone or in combination.

[0138] An electrode tab may be formed extending from each positive current collector 110 and negative current collector 120 to one end of the housing 170. The electrode tab may be soldered to one end of the housing 170 to form an electrode lead exposed to the outside of the housing 170.

[0139] Lithium secondary batteries can be manufactured in cylindrical (canister), prismatic, pouch, coin, and other shapes.

[0140] Preferred embodiments are presented below to describe the invention in more detail. However, the following examples are merely illustrative, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the invention. These changes and modifications should be included within the appended claims.

[0141] Example: Manufacturing of secondary batteries

[0142] (1) Positive electrode

[0143] "Positive electrode 1" is formed by continuously changing the mixing ratio of the precursors while forming precipitates.

[0144] The overall composition of cathode 1 is LiNi 0.8 Co 0.11 Mn 0.09 O2. The core and shell components of cathode 1 are composed of LiNi. 0.84 Co 0.11 Mn 0.05 O2 and LiNi 0.78 Co 0.10 Mn 0.12 O2.

[0145] A concentration gradient region is formed between the core and the shell. In this concentration gradient region, the Ni concentration decreases and the Mn concentration increases.

[0146] Under the first conditions in Table 1 below, a precursor solution containing a metal oxide precursor and a chelating agent is co-precipitated. The metal oxide precursor contains Ni, Co and Mn in a molar ratio of approximately 1:1:1, and the chelating agent contains ammonia and NaOH.

[0147] Then, under the second condition, the precursor solution was further co-precipitated to form "polymorphic NCM111".

[0148] Multi-shaped NCM111 has approximately LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The composition of O2. Polymorphic NCM111 contains granular primary particles in the central region, which is about 60% of the radius from the particle center, and rod-shaped primary particles in the peripheral region.

[0149] Under the third condition in Table 1 below, a precursor solution containing a metal oxide precursor and a chelating agent is co-precipitated. The metal oxide precursor contains Ni, Co and Mn in a molar ratio of approximately 5:2:3, and the chelating agent contains ammonia and NaOH.

[0150] Then, under the fourth condition, the precursor solution was further co-precipitated to form “polymorphic NCM523”.

[0151] Multi-shaped NCM523 has approximately LiNi 0.5 Co 0.2 Mn 0.3 The composition of O2. Polymorphic NCM523 contains granular primary particles in the central region, which is about 45% of the radius from the particle center, and rod-shaped primary particles in the peripheral region.

[0152] [Table 1]

[0153]

[0154] Denka carbon black was used as a conductive additive, and PVDF was used as a binder. The positive electrode active material (wherein the positive electrode active material particles are mixed in the weight ratios shown in Table 2 below), the conductive additive, and the binder were mixed in a weight ratio of 92:5:3 to form a positive electrode slurry. The positive electrode slurry was coated, dried, and pressed onto an aluminum substrate to form a positive electrode. The density of the pressed positive electrode was above 3.5 g / cc.

[0155] (2) Negative electrode

[0156] A negative electrode slurry was prepared by mixing 93 wt% natural graphite as the negative electrode active material, 5 wt% sheet-like conductive additive KS6, 1 wt% SBR as a binder, and 1 wt% CMC as a thickener. The negative electrode slurry was coated, dried, and pressed onto a copper substrate to form the negative electrode.

[0157] (3) Lithium secondary battery

[0158] The positive and negative electrodes obtained as described above are cut to appropriate sizes and stacked, with a separator (polyethylene, thickness: 25 μm) inserted between them to form an electrode unit. Each tab portion of the positive and negative electrodes is welded. The welded positive / separator / negative electrode assembly is inserted into a bag, and three sides of the bag are sealed (e.g., except for the electrolyte injection side). The tab portions are also included in the sealed portion. Electrolyte is injected through the electrolyte injection side, and then the electrolyte injection side is also sealed. Subsequently, the above structure is immersed for at least 12 hours.

[0159] The electrolyte was prepared by dissolving 1M LiPF6 in a mixed solvent of EC / EMC / DEC (25 / 45 / 30; volume ratio), followed by the addition of 1 wt% vinylene carbonate, 0.5 wt% 1,3-propensultone (PRS) and 0.5 wt% lithium bis(oxalate)borate (LiBOB).

[0160] The lithium secondary battery manufactured above was precharged by applying a precharge current (5A) corresponding to 0.25C for 36 minutes. After 1 hour, the battery was degassed and aged for more than 24 hours, and then subjected to formation charge-discharge (charging conditions: CC-CV 0.2C 4.2V 0.05C cutoff, discharging conditions: CC 0.2C 2.5V cutoff). Then, standard charge-discharge was performed (charging conditions: CC-CV 0.5C 4.2V 0.05C cutoff, discharging conditions: CC 0.5C 2.5V cutoff).

[0161] Comparative example

[0162] The multi-shape NCM111 and multi-shape NCM523 are replaced with single-shape NCM111 and single-shape NCM523 to manufacture the secondary battery in the same manner as in the above embodiments.

[0163] Single-shape NCM111 with LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The composition of O2, and the same particle shape in the central and peripheral regions.

[0164] Single-shape NCM523 with LiNi 0.5 Co 0.2 Mn 0.3 The composition of O2, and the same particle shape in the central and peripheral regions.

[0165] [Table 2]

[0166]

[0167]

[0168] Experimental Example 1: Using multi-shaped NCM111

[0169] (1) Evaluation of life characteristics at room temperature

[0170] The battery cells of Examples 1-8 and the Comparative Example were subjected to 500 repeated cycles of charging (CC-CV 1.0C, 4.2V, cut-off at 0.05C) and discharging (CC 1.0C, cut-off at 2.75V), then the percentage (%) of the discharge capacity at the 500th cycle relative to the discharge capacity at the first cycle was calculated to measure the life characteristics at room temperature. The results are shown in Table 3 below.

[0171] (2) Evaluation of penetration stability

[0172] The battery cells of Examples 1-8 and the Comparative Example were charged (1C, 4.2V, cut-off at 0.1C), then penetrated with a nail having a diameter of 3mm at a speed of 80mm / second, and evaluated according to the following criteria. The results are shown in Table 3 below.

[0173] <EUCAR hazard level>

[0174] L1: No problem with battery performance

[0175] L2: Irreversible damage to battery performance

[0176] L3: Electrolyte loss of the battery is less than 50%.

[0177] L4: Electrolyte loss of the battery is 50% or more.

[0178] L5: Fire or explosion

[0179] [Table 3]

[0180] Example 1 93.2％ L3 Example 2 94.1％ L3 Example 3 96.2％ L3 Example 4 96.9％ L3 Example 5 98.0％ L3 Example 6 98.5％ L3 Example 7 99.3％ L3 Example 8 99.9％ L3 Comparative Example 1 85.1％ L5 Comparative Example 2 86.4％ L5 Comparative Example 3 87.6％ L5 Comparative Example 4 89.3％ L4 Comparative Example 5 91.5％ L4 Comparative Example 6 92.9％ L4

[0181] As shown in Table 3, compared with the Comparative Example using single-shaped secondary positive electrode active material particles, in the Examples using multi-shaped secondary positive electrode active material particles, both the life and penetration stability are improved.

[0182] Experimental Example 2: Changing the central region of multi-shaped NCM111

[0183] The secondary batteries of Examples 13-19 were manufactured in the same manner as in Example 3, except that the radius of the central region of the multi-shaped NCM111 was changed to the radius from the center of the particle shown in Table 4 below.

[0184] The life and penetration characteristics of the secondary batteries of Examples 13-19 were evaluated by the above method, and the results are shown in Table 4 below.

[0185] [Table 4]

[0186]

[0187] As shown in Table 4, when the radius of the central region of the multi-shaped NCM111 is within the range of 20%-80%, penetration stability and lifetime are improved. When the radius is within the range of 40%-80%, penetration stability and lifetime are further improved.

[0188] Experiment Example 3: Using Multi-Shape NCM523

[0189] The secondary batteries of Examples 9-13 and the Comparative Examples were charged once (CC-CV 1.0C 4.2V 0.05C cutoff) and discharged once (CC 1.0C 2.7V cutoff). The capacity was measured and converted into energy density. After setting the battery capacity to 50% of the SOC (State of Charge), the output characteristics were measured using the Hybrid Pulse Power Characterization (HPPC) method.

[0190] Penetration stability was evaluated in the same manner as in Experimental Example 1. The results are shown in Table 5 below.

[0191] [Table 5]

[0192]

[0193]

[0194] The energy density, power output, and penetration characteristics of embodiments using multi-shape NCM523 are shown in Table 5.

[0195] Experiment Example 4: Changing the central region of multi-shaped NCM523

[0196] The secondary batteries of Examples 20-26 were manufactured in the same manner as in Example 12, except that the radius of the central region of the polymorphic NCM523 was changed to the radius from the center of the particle as shown in Table 6 below.

[0197] The lifetime and penetration characteristics of the secondary batteries in Examples 20-26 were evaluated using the methods described above, and are shown in Table 6 below.

[0198] [Table 6]

[0199]

[0200]

[0201] As shown in Table 6, power output and penetration stability are improved when the radius of the central region of the multi-shaped NCM523 is in the range of 20%-80%. Penetration stability and lifetime are further improved when the radius is in the range of 40%-70%.

[0202] Experiment Example 5: Assessing Penetration Safety Based on SOC

[0203] (1) Examples 27-30

[0204] The state of charge of the secondary battery in Example 10 was gradually reduced by 10% to prepare the secondary batteries of Examples 27-30.

[0205] The evaluation results of the penetration stability of the secondary batteries in Examples 27-30 are shown in Table 7 below.

[0206] (2) Comparative Examples 11-15

[0207] The state of charge of the secondary battery in Comparative Example 8 was gradually reduced by 10% to prepare the secondary batteries of Comparative Examples 12-15.

[0208] The evaluation results of the penetration stability of the secondary batteries of Comparative Examples 12-15 are shown in Table 7 below.

[0209] [Table 7]

[0210] Example 10 80％:20％ SoC 100% L3 Example 27 80％:20％ SoC 90% L3 Example 28 80％:20％ SoC 80% L3 Example 29 80％:20％ SoC 70% L3 Example 30 80％:20％ SoC 60% L3 Comparative Example 8 80％:20％ SoC 100% L5 Comparative Example 12 80％:20％ SoC 90% L5 Comparative Example 13 80％:20％ SoC 80% L5 Comparative Example 14 80％:20％ SoC 70% L4 Comparative Example 15 80％:20％ SoC 60% L4

[0211] As shown in Table 7, compared with the comparative example, the penetration stability under high SOC is significantly improved in the embodiment using multi-shape NCM523.

[0212] Experiment Example 6: Observe the surface and cross-section of the particles

[0213] Cross-sections of the multi-shaped NCM111, multi-shaped NCM523, single-shaped NCM111, and single-shaped NCM523 used in the examples and comparative examples were obtained by observing them using a scanning electron microscope (SEM). Figures 2-6 .

[0214] like Figure 2 As shown, in some embodiments, the multi-shaped NCM111 used has particles with different shapes in the central and peripheral regions. For example, the central region occupies approximately 60% of the particle radius, and the particles in the central region are observed to be granular. The peripheral region occupies the space excluding the central region, and the particles in the peripheral region are observed to be needle-shaped (needle-like).

[0215] like Figure 3 and Figure 4 As shown, the traditional single-shape NCM111 has essentially the same particle shape in the central and peripheral regions.

[0216] like Figure 5As shown, in some embodiments, the multi-shaped NCM523 used has particles with different shapes in the central and peripheral regions. For example, the central region occupies approximately 45% of the particle radius, and the particles in the central region are observed to be granular. The peripheral region occupies the space excluding the central region, and the particles in the peripheral region are observed to be rod-shaped.

[0217] like Figure 6 As shown, the traditional single-shape NCM523 has essentially the same particle shape in the central and peripheral regions.

[0218] Experimental Example 7: Differential Scanning Calorimetry Measurement

[0219] The thermal properties of the multi-shaped NCM111 (C1), single-shaped NCM111 (C2), multi-shaped NCM523 (C3), and single-shaped NCM523 (C4) used in the examples and comparative examples were measured using differential scanning calorimetry. The results are as follows: Figure 7 and Figure 8 As shown.

[0220] like Figure 7 As shown, the thermal performance of the multi-shape NCM111 (C1) used in some exemplary embodiments is improved compared to the single-shape NCM111 (C2).

[0221] Specifically, a narrow peak of C2 at 61 J / g was observed near a temperature of 320 °C, while a broad peak of C1 at approximately 13 J / g was observed near a temperature of approximately 335 °C. Therefore, by using multi-shaped NCM111, the safety and reliability of secondary batteries at high temperatures can be achieved.

[0222] like Figure 8 As shown, the thermal performance of the multi-shape NCM523 (C3) used in some exemplary embodiments is improved compared to single-shape NCM111 (C2) and single-shape NCM523 (C4).

[0223] Specifically, a C2 peak of 61 J / g was observed near 323 °C, a C4 peak of 30 J / g was observed near 329 °C, and a broad C3 peak of approximately 23 J / g was observed near approximately 334 °C. Therefore, by using multi-shaped NCM523, the safety and reliability of the secondary battery at high temperatures can be achieved.

Claims

1. A positive electrode active material, comprising: Nickel-containing first positive electrode active material particles, and The second positive electrode active material particle contains nickel, wherein the concentration of nickel in the center of the second positive electrode active material particle is less than the concentration of nickel on the surface of the first positive electrode active material particle; The second positive electrode active material particles include primary particles aggregated together, wherein the primary particles have different shapes or crystal structures from each other. The different shapes include a first shape and a second shape, the first shape including granular or spherical, and the second shape including rod-shaped or needle-shaped. The second positive electrode active material particles include a first particle arranged in the central region and having a granular or spherical structure, and a second particle arranged in the peripheral region and having a rod-shaped or needle-shaped shape. The concentration of nickel on the surface of the first positive electrode active material particle is less than the concentration of nickel in the center of the first positive electrode active material particle.

2. The positive electrode active material according to claim 1, wherein the central region of the second positive electrode active material particle includes a region corresponding to 20%-80% of the radius from the center of the second positive electrode active material particle.

3. The positive electrode active material according to claim 1, wherein the nickel, manganese and cobalt contained in the second positive electrode active material particle do not have a concentration gradient region between the central portion of the second positive electrode active material particle and the surface of the second positive electrode active material particle.

4. The positive electrode active material according to claim 1, wherein the first positive electrode active material particle comprises a core portion, a shell portion, and a concentration gradient region located between the core portion and the shell portion.

5. The positive electrode active material according to claim 4, wherein the core portion and the shell portion each comprise a fixed composition.

6. The positive electrode active material according to claim 1, wherein the first positive electrode active material particle comprises a continuous concentration gradient formed from the center of the first positive electrode active material particle to the surface of the first positive electrode active material particle.

7. The positive electrode active material according to claim 1, wherein, In the first positive electrode active particle, the concentration of nickel in the metal elements other than lithium is 60 mol% or more.

8. The positive electrode active material according to claim 1, wherein, In the second positive electrode active material particles, the concentration of nickel, excluding lithium, is in the range of 48 mol% to 52 mol%.

9. The positive electrode active material according to claim 1, wherein the blending weight ratio of the first positive electrode active material particles and the second positive electrode active material particles is in the range of 9:1 to 1:

9.

10. The positive electrode active material according to claim 1, wherein, in differential scanning calorimetry (DSC) measurement, at a temperature above 200°C, the exothermic peak of the second positive electrode active material particles is below 40 J / g.

11. The positive electrode active material according to claim 1, wherein, The first positive electrode active material particle or the second positive electrode active material particle further includes a coating on its surface, and the coating includes at least one selected from the group consisting of Al, Ti, Ba, Zr, Si, B, Mg, P, alloys thereof and oxides thereof.

12. The positive electrode active material according to claim 1, wherein, The first positive electrode active material particle or the second positive electrode active material particle further includes a dopant, the dopant being at least one selected from the group consisting of Al, Ti, Ba, Zr, Si, B, Mg, P, their alloys and their oxides.

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